The present invention relates to a new and improved pallet changer having additional distribution and storage functions for fabrication installations or manufacturing plants equipped with a central control station, transfer stations at the conveyor or storage part of the system and address readers, and of the type possessing a rotatable part which can be rotated about a vertical axis and equipped with pallet guides and pallet feed or displacement devices for pallets having switching markers.
In heretofore known manufacturing installations equipped with conveyor lines the workpieces are clamped in a clamping zone upon pallets and successively transported at the conveyor line to one, several or all machines. Operatively associated with each machine is a pallet changer having two change positions and a transfer station at the conveyor line. The pallet changers usually possess a rotatable part which can be rotated through an angle of 180.degree. and having two pallet support guides and associated pallet feed or displacement devices. After a pallet has moved through the part of the conveyor line or path at the side of the machine, then it is either transported to the clamping zone or returned back to the start of the conveyor line. This pallet circulation is accomplished for such length of time until the pallet changer is free at the machine indicated by the central control station. The workpiece which has been finished at a machine is then reintroduced back into the conveyor line by means of the transfer station which is usually rotatable through an angle of 90.degree.. The effectiveness of the conveyor line or path as a storage is limited, since the total number of the pallets which can be received by the conveyor line is limited. Additionally, the pallets dam-up in front of the transfer stations and hinder one another, partially because of the return movement. The desired flexible charging of the machines with different types of workpieces and with priority workpieces is likewise unsatisfactory.
A somewhat improved effectiveness of the conveyor line is obtained by the provision of additional transverse conveyors, a primary conveyor loop being guided about the machines, which are arranged at the transverse conveyors. The pallet outfed by each machine through the action of a second transfer station associated therewith generally brings about a somewhat lesser damming-up of the pallets throughout the entire operation of the installation. The drawbacks attendant with such arrangement reside in increased equipment expenditure and cost owing to the need to provide additional transverse conveyors and transfer stations, and further, the impaired accessibility to the machines and pallet changers.
Furthermore, it is already known in this field of technology to design the conveyor path or line to possess a circular configuration. By means of a pallet changer located at the clamping and unclamping zone or station, it is possible to charge and unload a circular conveyor. Each machine has operatively associated therewith a further pallet changer which coacts with the circular conveyor. The expenditure constituted by three pallet changers and a circular conveyor is extremely high in order to, for instance, interlink two machines.
Now in German patent publication No. 24 35 622 there is described a fabrication installation having, apart from infeeding and return feeding primary conveyor paths or lines, an additional buffer conveyor line or path arranged along all of the erected machines parallel to the main or primary conveyor line. This prior art publication further discloses a technique of controlling priority pallets and routine pallets in conjunction with the buffer conveyor line, as well as the checking of the destination with the selection of the machines. This proposal for a flexible fabrication installation for small, suspended transportable pallets, however cannot be employed at conveyor or conveying lines for supported transportable heavy pallets.
In the case of fabrication installations having a pallet conveyor or feed device which travels upon rails, and which by elevationally adjusting its pallet support can service a shelf storage having large storage capacity, likewise requires for each machine a pallet changer having two change positions and a transfer station at the shelf storage (see the publication Werkstatt und Betrieb 107 (1974/8)). The pallet feed or conveyor device coacts with the clamping and unclamping zone, the shelf storage and the transfer stations in the shelf storage. Due to this arrangement there is afforded a flexible pallet flow, since priority workpieces can be directly inserted for machining. The pallet changers which are employed with such installation for larger sized pallets do not possess any storage capacity, so that particularly when used with manufacturing or fabrication installations having a multiplicity of installed machines, it is possible for the pallet feed device to become easily overloaded if at one or a number of machines there is only carried out an extremely brief amount of work at a workpiece, for instance post-finishing work and, consequently, there can occur standstill times.
Other fabrication installations having a pallet feed or conveyor device for small pallets and workpieces transported in containers, do not have this drawback, because between the transfer station of the shelf storage and the machine there is provided a combined buffer, charging and cleaning station, where the pallets are moved in a number of horizontal planes. The construction of such station is, however, not suitable for large pallets and cannot solve the objectives to which the present invention addresses itself.